1. Field of the Invention
The present invention relates to an electromagnetic coil assembly for use in an electromagnetic apparatus, such as an electromagnetic clutch for use in controlling the transmission of power from an automobile engine to a refrigerant compressor in an automobile air conditioning system. More particularly, it relates to the mounting structure for a thermal protection device, electrical wires, and caulking terminals in the electromagnetic coil assembly.
2. Description of Related Art
Referring to FIGS. 1 and 2, an electromagnetic coil assembly 4, which comprises a bobbin 1 and a coil 3, is known in the art. Bobbin 1 has a toroidal shape having a spool portion, which has an exterior open edge. Coil 3 is formed of electrical wire 2, which is wound around the spool portion. An electromagnetic coil assembly 4, for example, is used in an electromagnetic clutch 6 of a compressor 5 in an automobile air conditioning system, as shown in FIG. 3. Electromagnetic coil assembly 4 may be provided with a thermal protection device 7, e.g., a thermal fuse or a thermal switch, which is sensitive to high temperatures in electromagnetic clutch 6. Thermal protection device 7 isolates a power source, such as an automobile engine, to protect electromagnetic clutch 6 and compressor 5 when high temperatures due to friction are generated between the parts in electromagnetic clutch 6.
Referring again to FIGS. 1 and 2, thermal protection device 7 has a pair of leads, a first lead 7a and a second lead 7b, extending from either end of thermal protection device 7. An end of first lead 7a of thermal protection device 7 is connected to a wire end portion 2a of electrical wire 2 through a first caulking terminal 8. An end of second lead 7b of thermal protection device 7 is connected to a third lead 9, which is connected to the external power source (not shown), through a second caulking terminal 10. Thermal protection device 7, first lead 7a and second lead 7b, wire end portion 2a, and third lead 9 are disposed on a first end surface 1a of bobbin 1. A securing member 11 having a groove-shaped cross-section is fixed securely on first end surface 1a by adhesives. Thermal protection device 7 is fitted into the groove-shaped portion of securing member 11. A pair of projection portions 12a and 12b are formed on first end surface 1a. First lead 7a and second lead 7b are fixeded to projection portions 12a and 12b, respectively. Consequently, thermal protection device 7, as well as first caulking terminal 8 and second caulking terminal 10, is fixed to first end surface 1a of bobbin 1.
As shown in FIG. 1, electromagnetic coil assembly 4 is inserted into a core 5 ring 13 having a groove-shaped cross-section and a toroidal shape in plan view, such that thermal protection device 7 on first end surface 1a is positioned in an open end of core ring 13. Thereafter, a resin 14 is poured into the open end of core ring 13, and electromagnetic coil assembly 4 is fixed within core ring 13.
In electromagnetic coil assembly 4, the retention strength of thermal 40 protection device 7, first caulking terminal 8, and second caulking terminal 10 within core ring 13 is relatively low. Therefore, resin 14 may enter into the spaces between thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 and first end surface 1a of bobbin 1. Consequently, thermal protection device 7, first caulking terminal 8, and second caulking terminal 10 may be pushed upward by resin 14 entering into the spaces between these elements, and as a result, these elements may not be covered by resin 14 and may be exposed outside core ring 13. Thus, when electromagnetic coil assembly 4 disposed in core ring 13 is equipped with the parts, which comprise, for example, electromagnetic clutch 6, defects or damage may occur at thermal protection device 7, first caulking terminal 8, and second caulking terminal 10.
An object of the present invention is to reduce or eliminate the above-mentioned defects or damage, which may be encountered in known electromagnetic coil assemblies with thermal protection devices and caulking terminals.
In an embodiment of the present invention, an electromagnetic coil assembly for an electromagnetic apparatus comprises a bobbin, a coil, and a thermal protection device. The bobbin comprises a cylindrical tubular spool, and a pair of annular flanges projecting radially from the spool to form an exterior open edge. The coil is formed of an electrical wire. The electrical wire is wound around the spool between the flanges. The thermal protection device has a first and a second lead wires, each extending from one side thereof. The first lead wire is connected to one end of the electrical wire through a first connecting member. The second lead wire is connected to one end of a third lead wire of an electrical circuit through a second connecting member. The thermal protection device, the first lead wire, the second lead wire, the first connecting member, the second connecting member, and one end of the electrical wire, one end of the third lead wire are disposed and fixed on a first end surface of the bobbin. At least one securing member having a groove-shaped cross-section is fixed, e.g., welded securely or fitted pressedly, on the first end surface of the bobbin. The thermal protection device, the first connecting member, and the second connecting member are covered by the securing member.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following description of the invention with reference to the accompanying drawings.